Possible flare star in Bootis

astroguypaul

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Joined: 2013-03-15

Posted: April 3, 2013 - 12:09pm

Pat Hall and I are at York University in Toronto, Canada. Pat assigns his students the task of photographing a constellation each fall. He noticed that one photo showed an extra ~5th magnitude star near pi Bootis and omicron Bootis. This potentially is a previously unknown flare star in Bootis which has brightened by >100x!

The student's (Jasvinder Sandal) photos show 3 stars in a row near the bottom center. One image is attached but is unfortunately of relatively poor quality. It was taken with a Sony DSC-W570 18.2 Mpix handheld camera from Brampton, Ontario, Canada: 79.7667 W, 43.6833 N. DS0C1861 was taken on 2012-09-25 20:17:54 (exposure 2 seconds). The top/left star in that row is omicron Bootis, the middle is pi Bootis, and the bottom/right star in the row is the flare star; it is not present in the other photo or in constellation maps of Bootes.

Pat has estimated the position of the new object (dubbed "? Boo") as being the same distance south and west of pi Bootis as pi Bootis is south and west of omicron Bootis. So, in J2000 coordinates:

omi Boo: 14:45:14.46 +16:57:51.4

pi Boo: 14:40:43.57 +16:25:06.0

? Boo: 14:36:34.3 +- :01.1 +15:49:48.2 +- :02.5

Near that position on the sky there are 2 objects of potential interest. 2 arcmin away is LP 440-48, which is a V=17.4 high proper motion star (0.25"/year), and likely a late-type dwarf based on its red colors. 3.5 arcmin away is BD+16 2671, listed in SIMBAD as a V=10 possible F5 star.

Magnitude estimate for ? Boo is V=4.6, based on comparable brightness to omi Boo (V=4.60) but not as bright as pi Boo (a blended binary with V=4.53).

What leads you to believe that this isn't a hot pixel or other artefact?

I didn't see an image attached. Even if there were, the fact that it was a hand-held (!), 2 second exposure and that (apparently) the object only showed up at that time does not really warrant any serious follow-up.

Same thought crossed our minds be assured. The student did submit 2 images of different exposures a few minutes apart and the "flare" was present in the same location (simply different image). Also, being a hand held image, there was movement and thus all stars on the image have a distinct "pattern" (blurriness) which is shared by our possible flare star.

Thus the unknown object is not an artifact of the camera. Given that this occurred in Bootis, it seemed worthy to bring to the attention of the observing community

To see the candidate flare star, click the black-background image, then mouse over the full-size image and click the "red-green" option. The candidate flare star is the object on the right with a red circle but no green circle. (Red objects are detected on the submitted image; green are catalog objects.) Note that this image has had its background zeroed out so that an astrometric solution could be found.

To get the original images, toggle the "failed" button at upper right on the web page given above. Three new thumbnails appear: the two original images (DS0C1861, 2 seconds, and DS0C1875, 1/8 second), and a contrast-enhanced version of DS0C1875 which clearly shows the candidate flare star. Note that DS0C1875 was taken on 2012-09-25 20:45:50 (exposure 1/8 second).

It'd be great to hear if anyone sees anything similarly bright in this location when looking back over past images of their own, or in Palomar plates or other surveys.

A few months ago, there was an ATEL about a possible bright nova in Taurus, but it turned out to be a reflection of Aldebaran, which was only 3 degrees away from the purported nova. I see that Arcturus is only 6 degrees away from the anomalous feature in your image. I hate to be a cynic, but I have a feeling that the transient is just a reflection of Arcturus. Have you used this optical system to image other fields with very bright stars? If so, are there transients in those images, too? Also, do you have color data for the transient?

Dear Colin - no color data for the transient, unless someone knows how to extract color info from the original DSLR images online. And thanks for the reflected light suggestion; that's something we'll definitely have to investigate if no one else has seen anything this bright at this location in the past. Cheers, Pat

It occurs to me that we have two photos taken with different rotations of the camera relative to the sky but which show the object in the same location on the sky in both. I believe that rules out the simplest reflection scenario where the optical path inside the camera determines the location of the reflection. If that was the case, the reflection would have appeared at a different location on the sky when the camera was rotated.

Sorry for my delayed response; I've had a busy week. I tried blinking the two images, but there wasn't any discernible motion of the mystery object between the images. That probably rules out a satellite or aircraft (depending on the interval between images) as well as a reflection, as you pointed out.

I'm not sure what the mystery object is; it could be that I'm overlooking something here, so perhaps someone with more experience at widefield imaging could help out. Although I can't rule out the possibility that this is indeed a high-amplitude variable star, the odds of detecting such a bright new variable star with a handheld camera are remote, and I've learned the hard way to be cautious when I spot an unexpected transient in my data. Does anyone else have any thoughts?

I see that this transient was just reported in the JAAVSO. Congratulations! Have you tried contacting online astrophotography groups to see if anyone has images of Bootes taken around the time that the transient was detected? Given the popularity of wide-field astrophotography, I would think that someone out there must have useful data... if that person can be found.

As for the possible causes, I don't think that it's possible for this to have been a cataclysmic variable. I'm not aware of any CV that brightens by ~7 mag, only to rapidly fade almost instantly. Indeed, CVs undergoing a superoutburst stay bright for a while. So given a choice between the CV explanation and the flare-star explanation, I would definitely favor the latter. But wouldn't a flare star that bright have triggered Swift or some other satellite? Flare stars are very bright in X-ray wavelengths during a flare event.